The present invention relates to an automatic tool exchanging machine, provided for an NC machine such as machining center, for automatically exchanging a tool mounted to a spindle.
In general, a conventional automatic tool exchanging machine has a structure in which an tool exchanging arm is supported by a machine body so as to be freely rotatable and linearly reciprocally movable. The tool exchanging arm performs its rotational motion about an arm axis and performs its linear reciprocal motion in the arm axis direction. A pair of tool grasping portions for grasping tools are provided for both ends of the tool exchanging arm.
One of the basic or main objects of the machining center resides in the improvement in productivity, and particularly, it is an important technical matter to make short a time required for a tool exchanging operation by a tool exchanging machine (this requires about 20% time of the entire operation cycle time).
The tool exchanging operation for exchanging a tool mounted to a spindle by the tool exchanging machine includes the following detailed processes or operations.
(1) Operation for rotating a tool exchanging arm and grasping a used tool mounted to a spindle by one of tool grasping members (another one of tool grasping members grasps a tool to be next used).
(2) Operation for releasing the tool from a tool grasping member of the spindle for exchanging the used tool.
(3) Operation for linearly moving the tool exchanging arm in the axial direction of the spindle and remove a shank portion of the used tool from a tapered hole of the spindle.
(4) Operation for rotating the tool exchanging arm and exchanging the used tool with the tool to be next used (which may be called merely next tool hereinlater) aligned on the axial direction.
(5) Operation for linearly moving the tool exchanging arm and inserting the shank portion of the next tool into the tapered hole of the spindle.
(6) Operation for grasping the next tool by the grasping member of the spindle.
(7) Operation for rotating the tool exchanging arm and releasing the next tool mounted to the spindle from the tool exchanging arm.
Minor operations other than the above may be included thereafter.
The operations (1), (3)-(5) and (7) of the tool exchanging arm are functions generally provided for an automatic tool exchanging machine, and in a conventional structure, in order to linearly move the tool exchanging arm, a cam mechanism such as plate cam or positive motion cam as a motion conversion mechanism for converting a rotation motion of a rotation driving source to a linear motion of the tool exchanging arm has been used for a power transmission mechanism for transmitting a driving force from the driving source to the tool exchanging arm.
The conventional mechanism using the cam mechanism such as mentioned above has following defects or problems.
(a) Mechanical Problem
In the case of using the plate cam, it is necessary to press a contact against an outer contour of the cam and give a confining force to keep the operative connection. In order to keep this state, however, contacting pressure between the contact and the cam contour is increased, which will result in wearing of the cam or increasing of change of torque.
On the other hand, in the use of the positive motion cam, since a contact contacts the cam contour at two points, any confining force is not required. However, as the mechanism is operated at a high speed, slight elasticity of an actual part(s), loosening of an object member, and/or error caused in a manufacturing process will largely affect on the motion of the tool exchanging arm. This will result in shifting of the operation timing of the tool exchanging arm or shifting of the operational locus thereof from a predetermined locus, which may cause the tool exchanging mechanism to be erroneously operated.
(b) Space Problem
The positive motion cam comprises, for example, as shown in FIG. 10, a cam body 101 formed with a cam groove 100, a contact 102 engaged with the cam groove 100, and a cam follower member 103 to which the contact 102 is attached. According to such structure, in consideration of the side pressure applied to the contact 102, because it is impossible to reduce a curvature radius of the cam groove 100, it is difficult to locate such cam mechanism in a limited space.
(c) Cost Problem
Further, with reference to FIG. 10, it is necessary for the contact 102 to contact both side wall portions of the cam groove 100 at two points and it is also necessary to follow the motion of the contacting portion contacting to one side wall of the cam groove to the motion determined by the contact of the contacting portion contacting to the other one side wall. Accordingly, it is required to accurately work the side walls of the cam groove 100, and such groove working requires three-dimensional grooving and groove grinding workings, which require a much cost for installing a working equipment, and a cost for manufacturing each cam will be also increased.